It is known that, during the assembly of compressor guide blades, which are adjustable about their longitudinal axis, and the associated adjusting drive, these are aligned individually with respect to a reference groove arranged on the guide blade carrier by means of a device. This is necessary to ensure that all the blade airfoils of the ring of compressor guide blades always have identical stagger angles in order to ensure a synchronous incident flow at the downstream compressor rotor blades during operation. An asynchronous incident flow at the compressor rotor blades could lead to vibration excitation of individual blade airfoils of the rotor blades. This could, in the worst case, result in damage to the rotor blades. To avoid this undesired and possibly critical operating situation of the compressor, checking of the assembly quality by means of a final measurement of the angle position of all the adjustable guide blades is necessary before the compressor is put into operation.
Until now, the angle position of the guide blades has been measured by means of a universal angle gauge and an auxiliary device from outside the housing of the compressor. The auxiliary device, which was placed on the reference groove on the guide blade carrier, served as a stop for one measurement leg of the angle gauge. The rear side surface of an adjusting lever arranged on the rotatable compressor guide blade served as a stop surface for the second measurement leg of the angle gauge, from which the angle position of the guide blade could then be read off. Owing to the restricted spatial conditions at the compressor, and depending on the circumferential position of the compressor guide blade to be checked, there was the possibility of resulting reading errors and inaccurately placed measurement legs. This was possible in particular if the fitter had to work overhead. As a result of the erroneous inspection, there was the possibility of correctly set guide blades being unnecessarily adjusted into an erroneous position, or of incorrect positions of compressor guide blades not being identified. Overall, this had the possible result of stagger angles of the blade airfoils of rotatable guide blades being set in part non-uniformly as viewed over the circumference. A further source of errors which can lead to slightly asymmetrical setting of compressor guide blades are the tolerances as a result of the use of the auxiliary device.
The angle position may also be measured by means of a transportable but voluminous laser measurement device, as proposed for example in EP 1 895 267 A1. Although the known measurement device operates contactlessly with respect to the measurement surface, in the usually restricted environment this is possible only using a deflecting mirror which, in the rough industrial environment of such machines, has proven to be inadequately robust and thus susceptible to damage. Consequently, the laser measurement device requires relatively careful handling so as not to compromise the availability of the measurement device.
Furthermore, U.S. Pat. No. 4,597,187 discloses a measurement device, which corresponds to the design features of the claims, for measuring the angle of incidence of fixed compressor blades. Said measurement device is mounted on a table in order to be able to measure a preassembled but not yet mounted ring with blade airfoils of the compressor. The measurement device comprises a first contact point which is placed onto the leading edge or trailing edge of the blade airfoil to be checked. A rotatable cam disk with a measurement arm must then be pivoted such that two further contact points arranged on the measurement arm bear against the blade airfoil at the suction side or at the pressure side. The pivot angle of the cam disk is then detected by means of a sensor, which then indicates the angle of incidence of the respective blade airfoil. It is a disadvantage here that the measurement of the angle of incidence takes place directly on the blade airfoil. This makes it necessary to provide access to the blade airfoil for a person. The known device is therefore not suitable for determining the angular position of a compressor guide blade which is arranged in a compressor, and which is pivotable about its longitudinal axis, from the outside.
Similar devices for the direct measurement of the angle of incidence of compressor blades or steam turbine blades are known from SU 815466 and U.S. Pat. No. 4,718,172. Said devices have the same disadvantages as the device known from U.S. Pat. No. 4,597,187.